This invention relates to a digitally programmable delay control circuit.
Commonly assigned U.S. Pat. Nos. 6,377,094 and 6,664,832, entitled “Arbitrary Waveform Synthesizer Using a Free-Running Oscillator” disclose a digitally controlled arbitrary waveform synthesizer having a ring oscillator that provides a short-term stable time reference. A plurality of taps are provided to select edges (transitions) produced by the ring oscillator. In the arbitrary waveform synthesizer, a delay circuit is used to provide finer timing granularity for edge generation than one tap of the ring oscillator.
In signal generation applications, such as clock signal generation, the integrated circuit in which the signal generation circuitry is implemented may have undesirable variations or delays as a function of process, temperature and voltage. Most on-chip delay originates as transistor-sourced currents charging wiring and gate capacitances. This delay variation can span a range of more than 2.5:1. Such a range of delay uncertainty is unacceptable for certain applications where timing precision is critical. Existing efforts to deal with this delay uncertainty attempt to minimize the process variation on the chip, rather than measuring and correcting for it.
A programmable delay circuit is needed that is capable of precisely tracking variations in delays caused by process, temperature and voltage conditions of the integrated circuit.